This invention relates to a method of relieving a radio line and to a radio equipment in a synchronous digital hierarchy (SDH) network. More particularly, the invention relates to a method of relieving a radio line and to a radio equipment in an SDH network in which a radio transmission line is installed between optical transmission lines having a plurality of optical lines.
The world-wide trend toward the adoption of the SDH scheme for networks in optical transmission is continuing. FIGS. 16A, 16B are diagrams for describing the structure of a frame in SDH. This is for a transmission rate of 155.52 Mbps. One frame is composed of 9.times.270 bytes. The first 9.times.9 bytes constitute section overhead (SOH), and the remaining bits constitute path overhead (POH) and payload (PL).
The section overhead SOH is a section which transmits information (frame synchronizing information) representing the beginning of the frame, information specific to the transmission line (namely information which checks for error at transmission time, information for network maintenance, etc.) and a pointer indicating the position of the path overhead POH. Path overhead POH is a section which transmits end-to-end monitoring information within a network. The payload PL is a section which transmits 150 Mbps information.
The section overhead SOH is composed of repeater section overhead of 3.times.9 bytes, a pointer of 1.times.9 bytes and multiplex section overhead of 5.times.9 bytes. As shown in FIG. 17, the multiplex section refers to the section between terminal repeater units 1, 2. In a case where a number of transmission lines 3a.about.3c and repeaters 4a, 4c are provided between the terminal repeater units 1, 2, the repeater section refers to the section between both ends of one transmission line. The multiplex section is composed of a plurality of repeater sections.
As shown in FIG. 16B, the repeater section overhead has bytes A1.about.A2, C1, B1, E1, F1, D1.about.D3, and the multiplex section overhead has bytes B2, K1.about.K2, D4.about.D12, Z1.about.Z2. The meaning of each byte is illustrated in FIG. 18. The repeater section overhead transmits frame synchronizing signals (bytes A1, A2), an error monitoring signal (byte B1) for monitoring error in the repeater section, a fault specifying signal (byte F1) for specifying a fault in the repeater section, etc. The multiplex section overhead transmits an error monitoring signal (byte B2) for monitoring error in the repeater section, a changeover signal (byte K1) for changing over between a standby system and a working system, and a transfer signal (byte K2) for transferring the status in the multiplex section. The repeater section overhead and multiplex section overhead have a number of undefined bytes. Use of these bytes is entrusted to the communications manufacturer concerned.
In FIG. 18, NNI, UNI, STM, BIP, AIS and FERF signify network node interface, user network interface, synchronous transport module, bit interleaved parity, alarm indication signal and far end receive failure, respectively.
FIG. 19 is a diagram for describing the definitions of bytes K1 and K2. The first four bits b1.about.b4 of byte K1 indicate the type of changeover request. For example, these bits designate the changeover between operation and standby. The remaining four bits b5.about.b8 of byte K1 indicate the number of a working transmission line that has outputted a changeover request. The first four bits b1.about.b4 of byte K2 indicate the number of a working line, the fifth bit b5 indicates the changeover configuration, and the sixth through eighth bits b6.about.b8 indicate status of the transmission line.
FIG. 20 is a diagram for describing BIP. When corresponding bits of each pixel have been added on, BIP-8 identifies whether the result is an even number or an odd number. When corresponding bits at demarcation every three bytes have been added on, BIP-24 identifies whether the result is an even number or an odd number.
An SDH frame is thus constructed and application of SDH to networks is progressing mainly in optical transmission. There are cases in which such an SDH network incorporates a radio transmission line. For example, in a case where an SDH network is constructed across the ocean or across steep mountainous areas, an optical cable must be laid on the ocean floor or across mountainous terrain. However, the work for laying such cables is a major undertaking and requires great expenditure. When an SDH network is constructed in areas where the laying of cable is difficult, as in the case of the ocean floor or steep mountain ranges, an optical transmission line is laid as far as the entrance to the area, an optical transmission line is laid from the exit of the area and a radio transmission line is introduced between these two optical transmission lines.
FIG. 21 illustrates a first example of the arrangement of an SDH network in which a radio transmission line is introduced into an optical transmission line. In this case transmission is performed while terminating the redundant lines of the optical transmission line. The network includes optical transmission units 11a, 11b and radio units 12a, 12b. Optical transmission lines 13.sub.1W .about.13.sub.2P are laid between the optical transmission unit 11a and the radio unit 12a. The optical transmission lines 13.sub.1W, 13.sub.2W are working lines, and the optical transmission lines 13.sub.1P, 13.sub.2P are standby lines. The standby lines 13.sub.1P, 13.sub.2P become the working lines when failures develop in the working lines 13.sub.1W, 13.sub.2W, respectively. Identical data is transmitted on the working lines and standby lines.
Numerals 14.sub.1W, 14.sub.2W denote radio working lines provided in correspondence with the optical working lines 13.sub.1W, 13.sub.2W, respectively. Numeral 14.sub.P represents one radio standby line. The radio unit 12a terminates the optical standby lines and transmits data from the optical working lines 13.sub.1W, 13.sub.2W to the radio unit 12b via the radio working lines 14.sub.1W, 14.sub.2W. Further, when a fault has developed in one of the radio working lines 14.sub.1W, 14.sub.2W, the radio unit 12a transmits data, which has been accepted from the corresponding optical working line, to the radio unit 12b via the radio standby line 14.sub.P, thereby relieving the failed radio working line.
Optical transmission lines 15.sub.1W .about.15.sub.2P are laid between the radio unit 12b and the optical transmission unit 11b. The optical transmission lines 15.sub.1W, 15.sub.2W are working lines, and the optical transmission lines 15.sub.1P, 15.sub.2P are standby lines. The standby lines 15.sub.1P, 15.sub.2P become the working lines when failures develop in the working lines 15.sub.1W, 15.sub.2W, respectively. The radio unit 12b sends the optical working line 15.sub.1W and the optical standby line 15.sub.1P data accepted from the first radio working line 14.sub.1W or radio standby line 14.sub.P (at the time of failure), and sends the optical working line 15.sub.2W and the optical standby line 15.sub.2P data accepted from the second radio working line 14.sub.2W or radio standby line 14.sub.P (at the time of failure). As a result, identical data is transmitted to the optical working lines and optical standby lines.
In FIG. 21, an optical working line and an optical standby line form a pair, at two of such pairs are provided. However, N (.gtoreq.2) pairs are provided ordinarily. More specifically, the optical lines consists of N pairs of optical working lines and optical standby lines. The radio lines have radio working lines corresponding to the N-number of optical working lines as well as one radio standby line.
In accordance with this SDH network, radio working lines in the radio section need only be provided to correspond to the optical working lines. As a result, the number of radio channels can be made small and transmission efficiency can be improved. However, in a case where a fault occurs simultaneously in two radio working lines, only one line can be relieved. This results in a decline in network reliability.
FIG. 22 illustrates a second example of the arrangement of an SDH network in which a radio transmission line is introduced between optical transmission lines. In this case radio transmission is performed without terminating the redundant lines of the optical transmission line. The network includes the optical transmission units 11a, 11b and the radio units 12a, 12b. The optical transmission lines 13.sub.1W .about.13.sub.2P are laid between the optical transmission unit 11a and the radio unit 12a. The optical transmission lines 13.sub.1W, 13.sub.2W are the working lines and the optical transmission lines 13.sub.1P, 13.sub.2P are the standby lines. The standby lines 13.sub.1P, 13.sub.2P become the working lines when failures develop in the working lines 13.sub.1W, 13.sub.2W, respectively. Identical data is transmitted on the currently working lines and standby lines.
Radio working lines 14.sub.1W .about.14.sub.4W are provided in correspondence with the optical working lines and optical standby lines 13.sub.1W .about.13.sub.2P, respectively. Numeral 14.sub.P represents the single radio standby line. The radio unit 12a transmits data from the optical working lines 13.sub.1W, 13.sub.2W to the radio unit 12b via the radio working lines 14.sub.1W, 14.sub.3W and transmits data from the optical standby lines 13.sub.1P, 13.sub.2P to the radio unit 12b via the radio working lines 14.sub.2W, 14.sub.4W. Further, when a fault has developed in one of the radio working lines 14.sub.1W .about.14.sub.4W, the radio unit 12a transmits data, which has been accepted from the corresponding optical line, to the radio unit 12b via the radio standby line 14.sub.P, thereby relieving the failed radio working line.
The optical transmission lines 15.sub.1W .about.15.sub.2P are laid between the radio unit 12b and the optical transmission unit 11b. The optical transmission lines 15.sub.1W, 15.sub.2W are the working lines and the optical transmission lines 15.sub.1P, 15.sub.2P are the standby lines. The standby lines 15.sub.1P, 15.sub.2P become the working lines when failures develop in the currently working lines 15.sub.1W, 15.sub.2W, respectively. The radio unit 12b (1) sends the optical working line 15.sub.1W data accepted from the first radio working line 14.sub.1W or from the radio standby line 14.sub.P (at the time of failure); (2) sends the optical standby line 15.sub.1P data accepted from the second radio working line 14.sub.2W or from the radio standby line 14.sub.P (at the time of failure); (3) sends the optical working line 15.sub.2W data accepted from the third radio working line 14.sub.3W or from the radio standby line 14.sub.P (at the time of failure); and (4) sends the optical standby line 15.sub.2P data accepted from the fourth radio working line 14.sub.4W or from the radio standby line 14.sub.P (at the time of failure).
In FIG. 22, only two pairs of the optical working lines and optical standby lines are provided. However, N (.gtoreq.2) pairs are provided ordinarily. More specifically, the optical lines consist of N pairs of optical working lines and optical standby lines. The radio lines have radio working lines corresponding to the N-number of optical working lines and N-number of radio standby lines as well as one radio standby line.
In accordance with this SDH network, the transmission efficiency of the radio section is lower than that of the first arrangement described above but the reliability of the network is enhanced.
FIG. 23 illustrates a third example of the arrangement of an SDH network in which a radio transmission line is introduced into an optical transmission line. In this case radio transmission is performed without terminating the redundant lines of the optical transmission line. The network includes the optical transmission units 11a, 11b, the radio units 12a, 12b as well as optical transmission units 16a, 16b.. The optical transmission lines 13.sub.1W .about.13.sub.2P are laid (1) between the optical transmission unit 11a and the radio unit 12a and (2) between the optical transmission unit 11a and the optical transmission unit 16a. The optical transmission lines 13.sub.1W, 13.sub.2W are the working lines and the optical transmission lines 13.sub.1P, 13.sub.2P are the standby lines. The standby lines 13.sub.1P, 13.sub.2P become the working lines when failures develop in the currently working lines 13.sub.1W, 13.sub.2W, respectively. Identical data is transmitted on the currently working lines and standby lines. The optical working line 13.sub.2W and optical standby line 13.sub.1P are connected to the radio unit 12a, and the optical working line 13.sub.1W and optical standby line 13.sub.2P are connected to the optical transmission unit 16a.
The radio working lines 14.sub.1W, 14.sub.2W are provided in correspondence with the optical standby line 13.sub.1P and optical working line 13.sub.2W, respectively. Numeral 14.sub.P represents the single radio standby line. The radio unit 12a transmits data from the optical standby line 13.sub.1P and optical working line 13.sub.2W to the radio unit 12b via the radio working lines 14.sub.1W, 14.sub.2W. Further, when a fault has developed in one of the radio working lines 14.sub.1W, 14.sub.2W, the radio unit 12a transmits data, which has been accepted from the optical line corresponding to the radio working line that failed, to the radio unit 12b via the radio standby line 14.sub.P, thereby relieving the failed radio working line.
Optical transmission lines 17.sub.W, 17.sub.P are laid between the optical transmission unit 16a and the optical transmission unit 16, namely in parallel with the radio transmission lines. The line 17.sub.W is an optical working line provided to correspond to the optical working line 13.sub.1W, and the line 17.sub.P is an optical standby line provided to correspond to the optical standby line 13.sub.2P. The optical transmission unit 16a transmits data from the optical working line 13.sub.1W and optical standby line 13.sub.2P to the optical transmission unit 16b via the optical lines 17.sub.W, 17.sub.P.
The optical transmission lines 15.sub.1W .about.15.sub.2P are laid (1) between the optical transmission unit 11b and the radio unit 12b and (2) between the optical transmission unit 11b and the optical transmission unit 16b. The optical transmission lines 15.sub.1W, 15.sub.2W are the working lines and the optical transmission lines 15.sub.1P, 15.sub.2P are the standby lines. The standby lines 15.sub.1P, 15.sub.2P become the working lines when failures develop in the currently working lines 15.sub.1W, 15.sub.2W, respectively. Identical data is transmitted on the working lines and standby lines. The optical working line 15.sub.2W and optical standby line 15.sub.1P are connected to the radio unit 12ba, and the optical working line 15.sub.1W and optical standby line 15.sub.2P are connected to the optical transmission unit 16a.
The radio unit 12b (1) sends the optical standby line 15.sub.1P data accepted from the first radio working line 14.sub.1W or from the radio standby line 14.sub.P (at the time of failure), and (2) sends the optical working line 15.sub.2W data accepted from the second radio working line 14.sub.2W or from the radio standby line 14.sub.P (at the time of failure). The optical transmission unit 16b (1) sends the optical working line 15.sub.1W data accepted from the optical working line 17.sub.W, and (2) sends the optical standby line 15.sub.2P data accepted from the optical standby line 17.sub.P.
In FIG. 23, only two pairs of the optical working lines and optical standby lines are provided. However, N (.gtoreq.2) pairs are provided ordinarily. The radio lines consist of 2n-number of radio working lines corresponding to the n (&lt;N) optical working lines and n optical standby lines, as well as one radio standby line. The transmission lines provided in parallel with the radio lines have (N-n)-number of optical working lines and (N-n)-number of optical standby lines.
In accordance with this SDH network, network reliability can be improved over that of the second arrangement described above but higher construction costs are entailed because it is necessary to lay optical transmission lines in parallel with the radio lines.
Thus, a redundant configuration is adopted in which one channel among (M+1)-number of channels in a radio section is used as a standby line and this standby line is shared by the working lines on the remaining M-number of channels. The changeover between working and standby lines in the radio section is performed based upon parity added on uniquely in the radio section. The parity is, say, the byte B1 (see FIG. 18) in the repeater section overhead. When parity error has occurred at a rate greater than a set rate, a failure is judged to have occurred and a changeover trigger is generated to perform the changeover between working and standby lines. For example, in the SDH network of FIG. 21, (1) when the radio unit 12b detects the occurrence of failure in the radio working line 14.sub.1W, (2) the radio unit 12b is placed in a state in which it is capable of receiving data from both the radio working line 14.sub.1W and the radio standby line 14.sub.P. Next, (3) the radio unit 12b instructs the radio unit 12a, via an incoming standby line (not shown), to perform the working/standby changeover between the radio working line 14.sub.1W and the radio standby line 14.sub.P. (4) In response to the changeover command, the radio unit 12a performs the working/standby changeover of the lines in sync with a synchronizing signal and transmits data via the standby line 14.sub.P. (5) Thereafter, the radio unit 12b adopts the old standby line 14.sub.P as the working line, accepts data from this line and transmits the data to the optical lines 15.sub.1W, 13.sub.1P.
FIG. 24 is a diagram showing the configuration of a working/standby changeover controller, used when a failure develops in a radio line, in the radio unit 12b. The controller includes a priority setting unit 18a for setting the relief priority of radio working lines, a radio failure detector 18b for detecting failure in each of the radio working lines, a relieved-line decision unit 18c which, when failure has occurred in two or more radio working lines simultaneously or in succession, refers to the set relief priority and relieves the radio working line having the highest priority, and a line changeover control unit 18d for controlling changeover between the radio working line, which has been decided by the relief line decision unit 18c, and the radio standby line. If there is only one radio working line that has failed, the relief line decision unit 18c relieves this line even if its priority is low.
In the prior art, the order of priority of relief in a case where a plurality of lines have failed in a radio section is fixed or is the order in which the failures occurred. In other words, the prior art is such that relief of a radio line that has developed a fault is performed without giving any consideration to the redundant configuration of the optical transmission lines or the state of failure occurrence in the transmission lines.
However, when the conventional relief method is considered in terms of the overall network, there are many instances in which the method is not efficient. For example, with the conventional relief method, there are occasions where a line that should be relieved early on is not relieved whereas a line whose relief may be deferred to a later time is relieved first. In such case data communication cannot be carried out in a line exhibiting the worst conditions. This will be described in detail with reference to FIG. 21. Assume a situation in which the optical lines 13.sub.1W, 13.sub.1P open due to a failure of some kind, thereby interrupting line service, under which condition a radio failure occurs in the radio working line 14.sub.1W and then in the radio working line 14.sub.2W. According to the prior art in such case, the working/standby changeover is performed between the radio working line 14.sub.1W, which developed the radio failure first, and the radio standby unit 14.sub.P, thereby relieving the radio working line 14.sub.1W and not the radio working line 14.sub.2W. With this method, however, data communication becomes impossible on all lines. If radio working line 14.sub.2W were to have been relieved, communication of data from the optical line 13.sub.2W would become possible. Though the foregoing is for a case in which relief is performed in the order in which failure occurs, the results would be the same also in a case where the order of relief priority is fixed.
An example of another problem will be described with reference to FIG. 22. Assume that a radio failure has developed in the radio working line 14.sub.2W and then in the radio working line 14.sub.1W. According to the prior art in such case, the working/standby changeover is performed between the radio working line 14.sub.2W, which developed the radio failure first, and the radio standby unit 14.sub.P, thereby relieving the radio working line 14.sub.2W and not the radio working line 14.sub.1W. In other words, in a case where radio failures occur in radio working lines corresponding to an optical working line and optical standby line, the conventional method is such that a situation arises in which the radio working line corresponding to the optical standby line is relieved but not the radio working line corresponding to the more important optical working line.
Further, in a case where a radio failure occurs simultaneously in the radio working lines 14.sub.2W, 14.sub.4W corresponding to the two optical standby lines 13.sub.1P, 13.sub.2P, the conventional method relieves whichever radio working line developed the failure first. When the line conditions of the optical working line 13.sub.1W and optical working line 13.sub.2W are compared, it is found that there is a case in which the likelihood is high that the working/standby changeover will be performed because the line condition of the optical working line 13.sub.2W is poor. In such case the radio working line 14.sub.4W corresponding to the optical standby line 13.sub.2P should be relieved at a higher priority that the radio working line 14.sub.2W corresponding to the optical standby line 13.sub.1P. With the conventional method, however, the radio working line 14.sub.2W corresponding to the optical standby line 13.sub.1P is relieved but not the radio working line 14.sub.4W corresponding to the optical standby line 132.sub.1P.